1. Field of the Invention
This application pertains to method and apparatus for providing an anesthetic to a region of a patient's body.
2. Description of the Prior Art
a. Regional Anesthetics
Regional anesthetics are known to be attractive alternatives to general anesthetics for surgical procedures. For example, in knee surgery, it is possible to anesthetize the leg without need for a general anesthetic. Such procedures can enjoy better patient tolerance and faster recovery.
In a typical regional anesthetic procedure, a target nerve is identified for anesthetic treatment. For example, in a knee surgery, the femoral and sciatic nerves are preferred nerves for anesthetic treatment to numb the surgical region. For shoulder surgery, the brachial plexus nerve is the preferred nerve for anesthetic treatment.
With a target nerve identified, an electrically insulated needle with an electrode tip is advanced through the patient's skin and directed toward the suspected location of the nerve. The needle is coupled to a signal generator for creating a stimulating signal at the needle electrode. The physician determines when the needle is near the target nerve by observing a patient response to the stimulus at the needle electrode. For example, when the needle electrode is in close proximity to the sciatic nerve, the patient's foot moves in response to the stimulus. As used herein, “proximity” means close enough to the nerve that the electrical field from the electrode creates a detectable physiologic response in the nerve (i.e., creating neural impulses in the case of a stimulation signal or inhibiting the propagation of neural impulses in the case of a blocking signal as will be described). “Proximity” is a function of a number of variables including amplitude of the signal. A higher current field will electrically couple with a nerve from a greater distance.
When the physician is confident the needle is in close proximity to the target nerve, a local pharmacological anesthetic is delivered to the nerve. Such anesthetic may be injected through the bore of the needle to the target nerve. Alternatively, a catheter may be advanced through the needle bore to the target nerve. The needle is then removed over the catheter leaving the catheter in place at the target nerve. The local anesthetic is passed through the catheter to the target nerve. The catheter may be left in place for several days to permit delivery of anesthetic for an extended period. Such procedures are described in Gainer, et al., “Use of the Peripheral Nerve Stimulator and Standard, Unsheathed Needles in Performing Regional Nerve Blocks”, CRNA: Clinical Forum for Nurse Anesthetists, 3 (4) 186-9 (November 1992). Such procedures are also described in Klein, “Continuous Peripheral Nerve Blocks”, Anesthesiology, Vol. 103, pp. 921-1044 (November 2005) and Capdevila, et al., “Continuous Peripheral Nerve Blocks in Hospital Wards after Orthopedics Surgery”, Anesthesiology, Vol. 103, pp. 1035-1045 (November 2005).
Needles for performing the above-described procedure are commercially available. For example, such needles are available through B. Braun Medical, Inc. The STIMUPLEX® insulated needles come in 20-22 gauge sizes and are used for single injections. The larger CONTIPLEX® 18 gauge needle allows the passage of a 20 gauge catheter for extended pharmacological nerve blocks. Both types of needles attach to the STIMUPLEX® HNS 11 nerve stimulator. Such stimulators generate a stimulation signal at 1 or 2 Hz (switchable) with a maximum current at 5 mA.
Needles for facilitating nerve location during a peripheral nerve block procedure are described in U.S. Pat. No. 6,325,764 to Griffith et al. issued Dec. 4, 2001, U.S. Pat. No. 6,298,256 to Meyer issued Oct. 2, 2001 and U.S. Pat. No. 5,007,902 to Witt issued Apr. 16, 1991 (all incorporated herein by reference). Such needles are also described in U.S. patent application Publication No. 2004/0049231 A1 to Hafer published Mar. 11, 2004, U.S. patent application Publication No. 2004/0158304 to Cory et al. published Aug. 12, 2004 and U.S. patent application Publication No. 2005/0267545 A1 to Cory published Dec. 1, 2005 A1 (all incorporated herein by reference). The '545 application describes a low frequency stimulation (1 to 5 Hz) and a higher frequency background signal (500 to 10000 Hertz) at very low amplitude (less than 100 microamperes) for use in locating a nerve.
While the fore-going regional anesthetic procedure can have advantages over a general anesthetic, the procedure is not without disadvantages. An anesthesiologist finds the nerve through electrical stimulation and then administers the anesthetic. The anesthesiologist waits a period of time (e.g., 30 minutes) to confirm the effectiveness of the anesthetic procedure. This delay interrupts the efficient use of the anesthesiologist's time as well as efficient use of valuable operating room time. If the block is not working after the delay, salvage is problematic and the anesthesiologist usually resorts to a general anesthetic. Further, the procedure requires administration of fluid to a specific site. Such fluid may accumulate and present complications. Also, the procedure is not always effective. For example, the needle may stimulate a nerve but be separated from the nerve by a tissue plane. The administered anesthetic may simply push against the tissue plane and displace the nerve without numbing the nerve. In such cases, the procedure must be repeated or the patient put on a general anesthetic. Complications associated with regional anesthetics are described in Faccenda, et al., “Complications of Regional Anaesthesia Incidence and Prevention, Drug Safety: An International Journal of Medical Toxicology and Drug Experience, 24 (6) 413-42 (2001). Toxicity of local anesthetics is described in “Incredible Save Followed By Poor Communication” APSF Newsletter, pp. 63 and 64 (Winter 2005-2006) (describing an incidence of accidental delivery of an anesthetic into a vein resulting in cardiac arrest). Further, the volume of the local agent or the delivery needle itself can directly damage a nerve. Complications are also described in the afore-referenced article by Capdevila, et al.
U.S. patent application Publication No. 2006/0025832 A1 published Feb. 2, 2006 and U.S. patent application Publication No. 2006/0030899 A1 published Feb. 9, 2006 describe implantable systems for stimulating peripheral nerves to treat pain. No use of blocking frequencies is disclosed.
The present invention improves the prior art technique by applying alternative nerve blocking techniques to the target nerve.
b. Neural Blocking
Neural stimulation (such as the prior art stimulation noted above to verify placement of a needle in close proximity to a nerve) involves applying a signal to a nerve. The signal parameters (pulse width, frequency and amplitude) are selected to initiate neural action potentials to be propagated along the nerve to a limb (e.g., in the example given above, to cause foot movement).
Not all electrical signals applied to nerves are stimulation signals. Certain parameters can result in a signal that inhibits the nerve or blocks the propagation of action potentials along the nerve.
Many different forms of nerve blocking are known. Cryogenic nerve blocking of the vagus is described in Dapoigny et al., “Vagal influence on colonic motor activity in conscious nonhuman primates”, Am. J. Physiol., 262: G231-G236 (1992). Electrically induced nerve blocking is described in Van Den Honert, et al., “Generation of Unidirectionally Propagated Action Potentials in a Peripheral Nerve by Brief Stimuli”, Science, Vol. 206, pp. 1311-1312. An electrical nerve block is described in Solomonow, et al., “Control of Muscle Contractile Force through Indirect High-Frequency Stimulation”, Am. J. of Physical Medicine, Vol. 62, No. 2, pp. 71-82 (1983) and Petrofsky, et al., “Impact of Recruitment Order on Electrode Design for Neural Prosthetics of Skeletal Muscle”, Am. J. of Physical Medicine, Vol. 60, No. 5, pp. 243-253 (1981). A neural prosthesis with an electrical nerve block is also described in U.S. Patent Application Publication No. US 2002/0055779 A1 to Andrews published May 9, 2002. A cryogenic vagal block is described in Paterson C A, et al., “Determinants of Occurrence and Volume of Transpyloric Flow During Gastric Emptying of Liquids in Dogs: Importance of Vagal Input”, Dig Dis Sci, (2000); 45:1509-1516.
A frequency of a blocking signal is greater than a 200 Hz threshold and, preferably, greater than 500 Hz. Solomonow, et al. “Control of Muscle Contractile Force through Indirect High-Frequency Stimulation”, American Journal of Physical Medicine, Volume 62, No. 2, pages 71-82 (1983). Higher frequencies of as high as 5,000 Hz result in more consistent neural conduction block. Kilgore, et al., “Nerve Conduction Block Utilizing High-Frequency Alternating Current”, Medical and Biological Engineering and Computing, Vol. 24, pp. 394-406 (2004).
The nerve conduction block is applied with electrical signals selected to block the entire cross-section of the nerve (for example, both afferent, efferent, myelinated and non-myelinated fibers) at the site of applying the blocking signal (as opposed to selected sub-groups of nerve fibers or just afferent and not efferent or vice versa).
c. Use of Neural Blocking in Treatments
U.S. Pat. No. 5,188,104 to Wernicke et. al. Dated Feb. 23, 1993 describes sub-selection of fibers in a nerve by selecting a treatment frequency by which blocks certain nerve fiber types in the nerve while stimulating other nerve fiber types. Since certain fibers are stimulated while other fibers are blocked, there is no cross-section inhibition or blocking of the entire nerve and all of its nerve fiber types (for example, both afferent, efferent, myelinated and non-myelinated fibers).
U.S. Pat. No. 5,119,832 to Xavier issued Jun. 9, 1992 describes an epidural catheter with nerve stimulators. The '832 patent describes electrical stimulation (with or without concurrent drug treatment) in the epidural space to relieve pain. The electrical stimulation is low frequency (e.g., 0-120 pulses per second) and described as acting almost exclusively on the pain impulse traffic along the type C fibers in the spinal nerves.
U.S. Pat. No. 6,684,105 to Cohen et al. dated Jan. 27, 2004 (assigned to Biocontrol Medical Ltd.) teaches collision blocking in which a stimulation signal is applied to a nerves and an appropriately timed stimulus is applied to nerve to create neural impulses which collide with and thereby block propagation of the stimulation signal in a given direction. No therapy is achieved by the blocking. Such blocking avoids adverse side effects associated with permitting the stimulation signal propagating in an undesired direction to an organ not targeted for therapy.
U.S. patent application Publ. No. 2002/0055779 A1 published May 9, 2002 describes applying a high frequency block to a sciatic nerve to block undesired neural impulses which would otherwise contribute to spastic movement. With such spasm-inducing signals blocked, a therapy signal is applied to the muscle to stimulated desired muscle contractions. U.S. patent application Publ. No. 2005/0149148 A1 published Jul. 7, 29005 (assigned to Medtronic, Inc.) teaches using a blocking signal to avoid undesired side effect (i.e., pain) otherwise associated with a stimulation signal.
The use of a blocking signal as a therapy is described in various patent applications assigned to EnteroMedics, Inc. These applications pertain to use of a conduction block technology to a nerve for a treatment of a variety of gastro-intestinal disorders. These applications (incorporated herein by reference) include the following (all filed Sep. 29, 2003): U.S. patent application Ser. No. 10/674,330 (published Sep. 2, 2004 as Publication No. US 2004/0172086 A1); U.S. patent application Ser. No. 10/675,818 (published Sep. 9, 2004 as US Patent Application Publication No. US 2004/0176812 A1) and U.S. patent application Ser. No. 10/674,324 (published Sep. 2, 2004 as US Patent Application Publication No. 2004/0172085 A1). The same assignee is assigned U.S. patent application Ser. Nos. 10/752,994 and 10/752,940 both filed Jan. 6, 2004 with respective publication dates of Aug. 26, 2004 and Sep. 2, 2004, Publication Nos. US 2004/0167583 A1 and 2004/0172088 A1.
d. Accommodation
Blockage of a nerve can result in nerve accommodation in which other nerve groups assume, in whole in part, the function of the blocked nerve. For example, sub-diaphragm blocking of the vagus nerve may be accommodated by the enteric nervous system. U.S. patent application Ser. No. 10/881,045 filed Jun. 30, 2004 (published Feb. 17, 2005 as Publication No. US 2005/0038484 A1) (assigned to EnteroMedics, Inc.) (incorporated herein by reference) notes that a duty cycle of electrical impulses to the nerve to block neural conduction on the nerve can be adjusted between periods of blocking and no blocking in order to vary the amount of down regulation of the vagus nerve as well as preventing accommodation by the enteric nervous system.